This invention relates to an improved process for preparing linear olefins, particularly linear alpha olefins. More particularly, this invention relates to an improved process for oligomerizing ethylene or propylene or other alpha olefins to obtain oligomers which are linear olefins having from about 4 to about 20 carbon atoms. This invention also relates to a method for polymerizing or copolymerizing these linear olefins to produce higher molecular weight polymers.
U.S. Pat. No. 4,442,309, issued to Arthur W. Langer, Jr. on Apr. 10, 1984, is one of several patents assigned to Exxon Research & Engineering Company which discloses a method for preparing linear olefins of the type prepared according to the present invention. This reference discloses the polymerization of ethylene in the presence of a catalyst comprising the reaction product of a zirconium transition metal halide and an aluminum alkyl compound. The polymerization reaction takes place in the presence of a diluent such as chlorobenzene, dichlorobenzene, chlorotoluene, aromatics such as benzene, toluene, and xylene, and aliphatics such as pentane and heptane. The reaction temperature is about 75.degree. to 200.degree. C. and the ethylene pressure is above 50 psia while the mole ratio of ethylene to olefin reaction products is maintained above about 0.8 throughout the reaction. The process disclosed in the patent requires the step of killing catalyst activity after at least about 5 weight percent, based on diluent, of product olefin has formed by adding an agent or agents to kill the polymerization activity, thereby preventing or inhibiting deleterious side reactions. Typical killing agents mentioned are water, alcohol, carboxylic acids and phenols. The patent also states that a neutralizing agent must be used to neutralize the Friedel-Crafts activity of the catalyst which remains a problem even after polymerization activity is killed. Neutralizing bases which can be used include any Lewis base, i.e. alkali metal and alkaline earth metal hydroxides and carbonates, ammonium hydroxide, and ammonia among others.
Russian Inventor's Certificate No. SU104-701-A discloses a catalyst for ethylene oligomerization. The catalyst is comprised of zirconium salts of carboxylic acids and an alkyl aluminum sesquichloride. It is said that oligomerization can take place at 5 to 30 atmospheres and 60.degree. to 100.degree. C. in an aromatic solvent. When this reaction is carried out and the reactor is opened after completion thereof, the reaction mixture becomes yellow, fuming and the amount of olefin rapidly decreases with time due to Friedel-Crafts alkylation of the solvent. In order to prevent loss of the olefin, the reaction mixture has to be cooled and neutralized as suggested in the Langer, Jr. patent discussed above.
It is an object of the present invention to provide a method for producing linear olefins with a zirconium catalyst wherein the process can be carried out to completion without the necessity of prematurely killing the polymerization activity by the addition of a polymerization killing agent as characterized in the patent to Langer, Jr. It is another object of this invention to provide a process for the production of linear olefins which can be carried out to completion without the addition of neutralizing agents to the reaction mixture to prevent Friedel-Crafts type reactions which result in the loss of the olefin product. Still another object is to have an additive which will not kill subsequent polymerizations with other Ziegler catalysts.